1. Field of the Invention
The present invention relates to water-containing solutions of acrylic-functionalized organosilanes of the general formula I ##STR2##
in which R is a methyl or ethyl group, to a process for their preparation and to their use, inter alia for coatings, surfaces or intermediate layers.
2. Description of the Background
DE-B 1 270 716 describes aqueous solutions of methacryloxy- and acryloxyalkyltrialkoxysilanes. The concentration of the organosilanols and -siloxanols in the aqueous solutions is given as being from around 0.1 to 10% by weight. Their use for the treatment of glass fibers or fiber structures produced therefrom, such as rovings, fabrics or mats, is mentioned in particular. A description is given both of dilute solutions of from 0.25 to 1.5% by weight organosilane, for producing finishes on size-free fabrics or rovings, and of from 5 to 10% strength by weight solutions, for sizing freshly spun glass fibers.
In this context, an immersion method is used to deposit, from dilute solutions, monomolecular or multilayer coats (finishes) on the glass fiber, which finishes are anchored firmly to the fiber surface by means of Si--OH groups, with the formation of siloxane bonds.
From 5 to 10% by weight solutions employed in concentrated form, which are used for example for treating glass fibers after the spinning operation, by drawing the fiber over rolls, moving belts or pads which are impregnated with the treatment solution, lead to the formation of a film (size) which may have a positive effect both on the processing properties, such as the lubricity of the fiber and its twisting to give folded yarn, cable yarn or sliver, and on the properties of the subsequent product.
Owing to the double bond of the acrylic or methacrylic function at the organic radical, the silane molecules anchored firmly to the fiber surface by way of the siloxane bond are able to copolymerize with other double bonds of unsaturated resin systems and, after curing of the resins, are firmly integrated into the coherent phase or resin matrix.
By means of the composite structure produced by the organosilane at the phase boundary between glass fibers, or structures produced from them, and the surrounding matrix, entirely new sets of properties can be achieved in the resins used; for example, enhanced mechanical strength, improved electrical properties and better protection against the penetration of moisture.
One deficiency, however, is that solutions based on 3-methacryloxypropyltrialkoxysilanes can be stored only for a limited time. Furthermore, DE-B 1 270 716 discloses only those aqueous solutions based on 3-methacryloxy- or acryloxyalkyltrialkoxysilane which have been prepared using up to around 10% by weight of organosilane. In Example 1 of DE-B 1 270 716, gentle shaking of 1 part of acryloxypropyltrimethoxysilane with 20 parts of 0.1% strength acetic acid produced a homogeneous hydrolysate which was subsequently diluted to a 0.5% strength solution by adding 179 parts of water.
The time for which such solutions can be stored is also referred to below as service life. For example, from 0.1 to 1% strength by weight aqueous solutions of 3-methacryloxypropyltrimethoxysilane become cloudy after only 2 days. As the concentration of organosilane rises, the service life is dramatically reduced, and for a 10% strength by weight aqueous solution is only around 15 hours. As the service life increases, the monomeric and/or oligomeric organosilanols initially present form cyclic and linear polycondensates. As the chain length grows further, the solubility concentration of the polycondensates is also exceeded. Thus the solution first becomes cloudy, and then flocculation takes place. Cloudy and flocculated solutions are unusable for the treatment of glass fibers or fabrics produced therefrom.
In industrial processes, especially continuous processes, for example, during the spinning of glass fibers, it is usually necessary after a short time to replace the unusable solutions with new solutions; this leads inevitably to the complex necessity of keeping stocks of the solutions, and constitutes a considerable cost factor. Added to this is the expense of disposing of the unusable solutions.
In the preparation especially of concentrated solutions of 3-methacryloxypropyltrialkoxysilanes, a disproportionately long dissolving time is necessary until the clear point of the solution is reached. Another disadvantage is that, at concentrations less than 10% by weight of 3-methacryloxypropyltrialkoxysilane, it is no longer possible to reach a clear point.
However, for certain glass fiber sizes which comprise film formers, antistats and wetting agents as well as the organosilane, higher concentrations of organosilane are of advantage.
The object of the invention was therefore to provide a clear, aqueous solution of an organofunctional silane, the intention being that the organosilane in water, or reaction products formed in this case, i.e. monomeric, oligomeric or even polymeric hydrolysates and condensates, should be present in as high a concentration as possible, the clear point time (CPT) being as short as possible and the solutions having maximum service lives (SL), i.e. remaining free from clouding over a relatively long period.